In the prior art there is known the pretreatment of mineral alloy material, prior to feeding the material into an electric furnace, through a preheating arrangement, so that the feed mixture is heated in a separate preheating silo, where granular or lump-like (for example pelletized) feed mixture is heated and dried. Preheating is necessary in order to reduce the amount of energy needed for smelting the material in the electric furnace proper, and in order to volatilize certain impurities before feeding the material into an electric furnace. Preheated feed material also stabilizes the operation of the furnace. It is a well-known practice to use one or several preheating furnaces per each electric furnace. The material to be heated is fed in batches through a feed silo, by means of a distributor device, to the preheating silo, where the material is heated by a hot gas flow. Typically the hot gas mixture is fed into the preheating furnace through the bottom part thereof, so that it is distributed evenly inside the material bed. The preheating furnace is connected to the smelting furnace in a known fashion by separate feed pipe arrangements that extend through the ceiling of the smelting furnace to the interior of the electric smelting furnace, thus feeding the preheated material for smelting. Various preheating furnace arrangements are described for example in the publications FI 842577 A, FI 105236 B and FI 71088 B. In the prior art there also is known, from the publication U.S. Pat. No. 4,029,220, a rotary distributor by which material can be fed in a tank through the top part thereof, and said material can be distributed to suitable locations inside the tank. The distributor means include a distribution chute extending inside the tank at an inclined angle α with respect to the vertical direction for distributing the material to the interior of the tank. Further, the distributor means include a rotation frame that can be rotated around a central vertical rotation axis. The rotation frame essentially includes a vertical inlet channel that extends to the interior of the tank. The distribution chute is attached to the lower part of the rotation frame. An inlet channel opens upwardly for receiving any gravitationally moving loose material, and downwardly for discharging said loose material to the distribution chute, and further through the distribution chute to the tank. Moreover, the distributor device includes a circular support frame that is attached horizontally to the rotation frame and concentrically with respect to the central vertical rotation axis. A number of support rollers is connected to the tank, so that the axes of the support rollers are positioned radially in relation to the central rotation axis. The support rollers are arranged to be in contact with the support frame for supporting the rotation frame on the support rollers and for bearing mounting the rotation frame to be rotary in relation to the tank. Power means are arranged to rotate the rotation frame. In the distributor known from said US publication, the rotation frame is provided with a gear ring, which the power means rotate by intermediation of a gear wheel.
A drawback with the known distributor means is that the gear ring and the gear wheels are expensive components that are easily susceptible to damage, and they are cumbersome to maintain and replace.